Application of the hottest weighing and balancing

Weight and balance system (WBS) is a very important system for large aircraft, which is mainly used to measure and calculate the weight and center of gravity position of the aircraft in real time, so that it can continuously feed back the weight and center of gravity of the aircraft, transmit information to the flight control system, and adjust the flight attitude during airdrop by the flight control system; Display the weight and center of gravity of the aircraft to the crew in real time through the display; At the same time, the security of the system is improved by over limit alarm (visual and auditory)

accurate and real-time measurement of aircraft weight and center of gravity is very important. The increase of aircraft weight will change the center of gravity of the aircraft, reduce the commercial load efficiency of the aircraft, and seriously affect flight safety. For example, replacing the paint on the surface of Boeing 747 fuselage will result in a total weight difference of hundreds of kilograms between the old and new paint. Weight change may lead to:

(1) the actual center of gravity deviates, and the tail rubs against the runway when the aircraft is pulled up, causing a fire

(2) the actual center of gravity is forward, and it is still difficult to pull up when the aircraft rushes to the end of the runway

(3) the center of gravity of the helicopter deviates from the rotor axis, making it difficult for the pilot to operate the aircraft

at present, many foreign large aircraft models such as Airbus and Boeing have adopted WBS system to automatically measure the weight and center of gravity data of aircraft. The relevant WBS system requirements are described in detail in ISO international standards, and the detailed design and performance requirements of the system are also described in ARINC international standards. []

for weight measurement, generally, the way of using the top hole under the belly of the aircraft as the load-bearing point, using the spoke sensor as the measuring part between the top hole and the load-bearing point, and lifting the aircraft by the hydraulic jack to make the sensor load-bearing is adopted. This method of measurement is cumbersome, not real-time, and the degree of digitization is low. The acquisition of the center of gravity is mainly based on the manual measurement and manual calculation of special ground staff. The WBS system developed by Taiyuan Aviation Instrument Co., Ltd. has the following advantages compared with the traditional weight measurement and center of gravity calculation methods:

(1) provide real-time weight and center of gravity data suitable for flight operation for large aircraft

(2) when the weight center of gravity and attitude change, it can correct and display the latest weight center of gravity data in real time

(3) accurate weight and center of gravity management can give fault alarm display when the weight and center of gravity exceed the limit

development of WBS system

foreign WBS system was applied in large aircraft in the early 1990s by word amplification, collection and closed-loop control, mainly for aircraft overall weighing. WBS system uses strain sensors and pressure sensors

because the aircraft weighing and balancing system can determine the aircraft weight and center of gravity in real time, and strictly control the safety and economic indicators of aircraft operation, it has gradually been favored by large aircraft. The U.S. military transport aircraft C-130, Boeing 777 and Airbus A340 have adopted this system. Among them, the latest Boeing 777 uses the weighing and balancing system of crane company of the United States, which effectively improves the overall performance of the aircraft, improves the loading and unloading efficiency, and greatly reduces the maintenance cost

basic function composition of weighing and balancing system

system module mainly includes weighing and balancing computer, sensor data management and display computer, pressure sensor group in landing gear hydraulic buffer (for aircraft overall weighing) [2] and cargo tank floor resistance strain sensor group (for cargo tank floor weighing). The main function of the system is to receive various signals, calculate and output the real-time weight and center of gravity data, and output the corresponding weight and center of gravity information to the flight control system for flight state control

the system mainly realizes two parts of functions. The first part is the real-time weighing and center of gravity calculation of the aircraft under ground conditions; The second part is the real-time weighing and center of gravity calculation of cargo tank floor

design principle of weighing and balancing system

1 design principle of aircraft ground overall weight center of gravity measurement

(1) weighing working principle

the total weight of the aircraft is supported by the landing gear fluid under the fuselage, such as wires, switches, electrical enclosures and other pressure buffers. The pressure borne by each hydraulic buffer plus the weight of aircraft tires, braking systems and steering beams is the total weight of the entire aircraft. A set of weighing sensors installed on the hydraulic buffers of each landing gear of the aircraft can accurately measure the pressure borne by each hydraulic buffer, so as to realize the accurate weighing of the aircraft

(2) balance working principle

balance is mainly to measure the center of gravity of the aircraft. On the ground, the center of gravity position of the aircraft is calculated by comparing the total weight of the aircraft with the sum of the moments of the hydraulic buffers of each landing gear relative to the reference position. The position of the aircraft center of gravity should be controlled within the range required by the aircraft manufacturer, which is generally expressed as a percentage of the aircraft Mac

(3) system composition

the system is mainly composed of weighing balance computer (WBC), sensor data management and display computer (SDM) and sensor module (LS). The real-time display of weight and center of gravity is completed by the sensor data management and display computer

· weighing and balancing computer (WBC)

the main function of the weighing and balancing computer is to receive, solve and process signals through the central processing unit, output the calculated weight and center of gravity signals in real time, and provide fault indication and audible alarm signals. The computer includes the algorithm of weight and center of gravity in various cases, the discrimination of over limit, and the algorithm of solving and correcting the sensor signal

· sensor data management and display computer (SDM)

sensor data management and display computer is used to display and store aircraft data. In order to ensure the interchangeability of the weighing and balancing computer, the weight center of gravity and other data of each aircraft when it is unloaded, the position of each weighing sensor and the calibration data of the sensor will be stored in the sensor data management and display computer. The data exchange will be realized through the communication with the weighing and balancing computer, and the stored data will not be lost due to the power failure of the system

· sensor module (LS)

the sensor module adopts a large pressure sensor, which is placed in the landing gear hydraulic buffer and forms a whole with the hydraulic buffer. It is used to feel the pressure in the aircraft hydraulic buffer and send it to the weighing and balancing computer after processing

2 the design principle of the real-time measurement system of aircraft cargo cabin weight and center of gravity benefits from its excellent performance

in the process of loading and unloading cargo, the movement of cargo in the cargo cabin causes the moment to change. At this time, the instantaneous center of gravity change of the aircraft will make the aircraft in an unstable state. The system can provide real-time data of the weight and center of gravity of the cargo hold of the transport aircraft

(1) sensor selection

the digital resistance strain type load cell with relatively mature technology and easy implementation and maintenance is adopted, which has simple structure, reliable and stable performance and high sensitivity. The accuracy of the sensor is affected by many factors, such as the accuracy of strain gauge, the material and structure of elastomer, the material of adhesive, sealing material, signal processing circuit and so on. The existing WBS system is designed under the ground static weighing condition, and its accuracy can reach 0.1% after the sensor data calibration

(2) design of sensor assembly

the resistance strain weighing sensor assembly is mainly composed of three parts: bridge detection circuit composed of resistance strain gauge, elastomer and digital processing circuit

the detection circuit uses four resistance strain gauges to form a Wheatstone bridge. In order to improve the measurement sensitivity, two corresponding strain gauges are usually used, and the strain gauges relative to the bridge arm are placed at the positions of tensile stress and compressive stress respectively, which are used for the detection of gravity signals. The assembly of strain gauge and elastomer generally adopts adhesive type, and the bridge circuit is pasted on the stress sensitive part of elastomer [4]

the elastomer used for strain type load cell is usually elastic beam type according to the requirements of measurement mode and measurement range in WBS system. The design of elastomer is first to select materials, make the finished elastomer, stick the electric bridge on the elastomer, and then make the digital processing circuit, combine the three parts into a finished product, install it at the connection between the main beam and the deck and the guide rail, and develop a suitable elastomer according to the structure of the actual connection position. The calibration of the sensor is completed before delivery, which is convenient for replacement and maintenance

the digital processing circuit is used to collect, solve and correct the signals output by the bridge, and finally output them to the weighing and balancing computer in the form of bus

(3) distribution of load cell components

the load-bearing parts of the cargo hold of the aircraft include the deck and guide rail. The deck is generally divided into blocks. In addition, it includes several guide rails. There is a load-bearing main beam at the bottom of the deck and guide rails. Resistance strain weighing sensors are arranged at the connection between the main beam and the deck and guide rails. The location is easy to select, the fixation is convenient, and the maintenance and data calibration are convenient

the sum of the weight felt by all the load cells arranged in the cargo hold is the total weight of the loaded goods and personnel, and the location of the sensors is fixed and known, so the change of the center of gravity can be calculated at any time. The weight calculation can be corrected by receiving the attitude and acceleration signals output by the inertial navigation system in real time

3 the design and implementation of the system combining the overall weighing of the aircraft on the ground and the real-time weighing of the cargo hold

under the ground condition, before loading the cargo, the overall weight and center of gravity of the aircraft are sensed by the pressure sensor arranged in the hydraulic buffer and measured and calculated by the weighing balance computer. This information is transmitted to the sensor data management and display computer for display, and the information is recorded according to the standard data format; At the same time, through the bus, the weight center of gravity information is output to the cargo airdrop management computer in the cargo airdrop system for aircraft cargo monitoring; Output the weight and center of gravity information to the flight control system for aircraft state control; The flight control system can adjust the aircraft according to the weight and center of gravity information to adjust the center of gravity to a suitable position. After loading the cargo, it is sensed by the resistance strain weighing sensor arranged on the load-bearing girder under the cargo hold floor and guide rail, and the increased weight is measured and calculated by the weighing balance computer. The changed aircraft center of gravity can be calculated. The weight and center of gravity data are output to the arrival airdrop computer and flight control system in real time, and transmitted to the sensor data management and display computer for storage

during the flight, the location and weight of the loaded goods have been recorded in the storage unit; And it can receive information about fuel flow, consumption and transfer from the fuel consumption computer; The relative position of the resistance strain weighing sensor in the cargo hold is fixed. After the gravity correction calculation is carried out according to the pressure and attitude received by each weighing sensor and the three-axis acceleration signal, the new aircraft center of gravity position can be obtained in real time according to the center of gravity calculation formula, so that the pilot can quickly grasp the dynamic balance of the aircraft and ensure flight safety

conclusion

with the rapid development of the national economy and the increase of military needs, the proportion of large air cargo in transportation does not hydrolyze, which can significantly increase the toughness of nylon, and the weighing and balancing system is a necessary and important system in air transportation. Therefore, the development and application of this system in large aircraft will reduce ground handling